1. Field of the Invention
The present invention relates to a superconductor layer and a method of manufacturing the same, particularly, to a superconductor layer containing oxide superconductor and a method of manufacturing the same.
2. Description of the Related Art
Oxide superconductors with high critical current density are expected to be used in, for example, a fusion reactor, a magnetically levitated train, an accelerator and a magnetic resonance imaging (MRI) apparatus, and have already been put to a practical use in some fields. Oxide superconductors include, for example, bismuth series oxide superconductors and yttrium series oxide superconductors. Particularly, yttrium series oxide superconductors exhibit satisfactory characteristics within a magnetic field and, thus, attract keen attentions as a material that is closest to the practical use.
A superconductor layer made of yttrium series superconductor can be manufactured by, for example, a pulsed laser deposition (PLD) method, a liquid-phase epitaxy (LPE) method, or an electron beam (EB) method. In recent years, a metal-organic deposition (MOD) method, which can be performed in a non-vacuum atmosphere and permits a low manufacturing cost, attracts attention, and vigorous research is being made on the MOD method mainly in the United States of America. Particularly, good properties are repeatedly reported in respect of the MOD method using a fluoroacetate such as trifluoroacetate (TFA), which is hereinafter referred to as TFA-MOD method.
According to the TFA-MOD method, a superconductor layer is formed by the following manner. First, trifluoroacetates of metals that constitute the superconductor are prepared by using trifluoroacetate and aqueous solutions of metal acetates, followed by dissolving the trifluoroacetate of metals in an organic solvent to obtain a coating solution. Then, a substrate is coated with the coating solution to obtain a coating film, and the coating film thus obtained is subjected to a calcining process in a humidified oxygen atmosphere so as to form a precursor that contains elements to be used as constituents of oxide superconductor. Further, the coating film is subjected to a firing process in a humidified atmosphere so as to bring about crystallization of the precursor. In other words, crystals of oxide superconductor are allowed to grow on the substrate. Thereafter, an annealing in an oxygen atmosphere is performed. A superconductor layer is formed by the process described above.
According to the method described above, it is possible to easily obtain a superconductor layer exhibiting a high critical current density Jc. However, the present inventors are of the opinion that the TFA-MOD method is capable of achieving a still higher critical current density Jc.